A wire-bonding apparatus is used for connecting between a lead of a substrate and a pad of a chip with a fine wire, for example. The wire bonding is performed in the following manner. Specifically, a wire along with a tool for wire bonding is caused to move down toward a lead. The wire and the tool are first moved down at high speed, and then slowed down when they come closer to the lead. The low-speed lowering at this time is referred to as first searching (1'st searching). Then, the wire is pressed against the lead by a tip of the tool, and the wire and the lead are bonded while ultrasonic vibration is applied. This bonding is referred to as first bonding (1'st bonding). After the first bonding, the tool is moved upward to feed the wire and moved above a pad while forming an appropriate loop. When the tool comes above the pad, the tool is moved down. The wire is first moved down at high speed, and then slowed down when it comes closer to the pad. The low-speed lowering at this time is referred to as second searching (2'nd searching). Then, the wire is pressed against the pad by the tip of the tool, and second bonding (2'nd bonding) is performed by bonding the wire and the pad while ultrasonic vibration is applied. After the second bonding, the tool is moved upward while the movement of the wire is stopped by a wire clamper to cause the wire to be disconnected at the second bonding point. Repeating this, a plurality of leads of a substrate and a plurality of pads of a chip are connected. Here, heating may be performed appropriately during the first bonding and the second bonding. Moreover, the first bonding may be performed to the pads, and the second bonding may be performed to the leads.
As described above, in the wire bonding, two bonding including the first bonding and the second bonding are performed. Unfortunately, however, there is a case in which the first bonding or the second bonding is not normally performed. Further, there may be a case in which, as the first bonding is insufficient, the wire is separated from the lead at the stage of the loop formation before the second bonding. There may also be a case in which the wire is disconnected in the middle of the loop formation even if the first bonding has been normally performed. These phenomena are collectively referred to as nonsticking, and detection of such nonsticking is required to be performed at an early stage. In order to detect nonsticking, a voltage or a current is applied between a side of the substrate and a side of the wire of the tool, and nonsticking is determined based on whether or not a resistance component, a diode component, and a capacitance component between these sides are normal.
Known methods of wire bonding include a ball bonding method and a wedge bonding method.
In the ball bonding method, a gold wire or the like with which a FAB (Free Air Ball) may be formed by high-voltage spark or the like is used, and a capillary having a chamfer portion rotationally symmetric about an axis along a longitudinal direction at its tip is used as a tool.
In the wedge bonding method, an aluminum wire or the like is used and any FAB is formed, and a tool for wedge bonding having a wire feed guide and a pressing surface at its tip is used as a tool for bonding instead of a capillary. In the wedge bonding, at the tip of the tool, the wire is fed along the wire feed guide at an angle on a side of the pressing surface, and a side surface of the wire is pressed against a bonding target with the pressing surface so as to perform bonding. Therefore, the wire projects laterally from the pressing surface by the tip of the tool, and the tip of the tool is not rotationally symmetric about the axis along a longitudinal direction.
As the tip of the tool for wedge bonding is not rotationally symmetric, there is a case in which a direction of the wire feed guide may not be aligned with a direction of connection of the wire as it is depending on the arrangement of the pads and the leads. Accordingly, a bonding head that holds the tool is configured as a rotary type, or a bonding stage that holds the bonding target is rotated. Thus, there is proposed a method of using a capillary having a rotationally symmetric tip, and of pressing the side of the wire with the tip of the capillary to perform bonding.